1 At present, the main surface treatment technologies at home and abroad include surface pretreatment, electroplating, autocatalytic deposition, surface conversion, chemical vapor deposition, vacuum evaporation, sputtering technology, ion plating, ion implantation, electron beam surface modification, and laser beam surface modification. Properties, surface heat treatment, chemical heat treatment, hot dip coating, thermal spraying, surfacing, sol-gel method, polymer coating, etc. Due to the emergence of new materials and new processes, physical vapor deposition technology including vacuum evaporation, sputtering technology, ion plating, ion implantation and other applications are increasingly widespread, and the effect is very satisfactory, which is representative of the development of surface technology in recent years. Pan Guoshun pointed out that the use of ion plating technology can significantly improve the tribological properties of the workpiece and improve its service life. It has been suggested that PVD coatings can be used to replace lubricants. British D. Walton and AJ Goodwin have done similar dry friction experiments. The results show that the results are very good. The experiments by DaYungWang et al. also show that the MoS2Ti film shows good results. Solid-like lubrication, reducing friction coefficient and extending friction life. The development of physical vapor deposition technology has the application object to expand continuously, the substrate temperature of deposition is lower, and it is new, composite and multi-layered, which constantly changes the preparation process and improves the tribological properties.
With the development of technology, people have put forward higher requirements for gear transmission. Traditional gear surface heat treatment processes have been difficult to meet the needs of development, and some new surface strengthening theories and techniques have been applied to the field of gear research to meet the development requirements. For example, in modern machines, especially in the aerospace, aerospace and submersible fields, high-performance gears can withstand increasing torque and high power, with large gear ratios, high efficiency, low noise, light weight and small size. The solution to this problem is to use a composite surface treatment that uses two separate surface/subsurface modification processes to surface the gears to produce composite mechanical, metallurgical and chemical properties that cannot be achieved by any single process. The soft substrate is covered with two hardened layers to improve surface hardness, strength and wear resistance, such as NiN and TiO2 coatings. The nitrided gear has a deep hardened layer with certain hardness, wear resistance and residual. The stress constitutes an ideal support for the super-hard film; on this basis, a super-hard film such as TiN or CrN is deposited, and the load-bearing capacity far exceeds that of a single super-hard film or nitride layer. The hard substrate is first formed on the soft substrate, and then the soft plating layer is covered, which is more effective in improving the surface tribological properties.
M.Murakawa also uses physical vapor deposition (PVD) technology to coat the surface of the gear with a layer of WC/C film. In the case of oil-free lubrication, its service life is three times that of the quenched and ground gear. D. Walton's research results also have The same conclusion came out. Timken uses physical vapor deposition (PVD) technology to coat a surface of the gear with a coating thickness of about 2 m, named ES200. The gear's scuffing ability is improved by 70 compared to hardened gears. In the research report, many details are still in secrecy, especially Timken, which refers to the coating as ES200. Domestic scholar Huang Hua? The research indicates that the NiP alloy layer on the gear surface can increase the contact fatigue strength by 1.457 times, and the NiCo alloy layer on the gear surface can increase the contact fatigue strength by 1.095 times, but these conclusions are simulated on the contact fatigue test machine. The experimental results of coating on real gears are different.
The author believes that the use of coating technology on the surface of the gear plating composite coating, in order to improve the surface strength of the gear and anti-wear and anti-wear performance, so as to achieve less use of lubrication medium or no lubrication medium, the purpose of establishing an environmentally friendly gear transmission, should It works. To this end, the author made a corresponding basic experimental research on the gear test bench built by himself.
2 Experimental part 2.1 Test piece, experimental equipment and experimental conditions 2.1.1 Pair of cylindrical spur gears of gear test piece, modulus: m=1.75; drive gear: number of teeth = 17, outer diameter = 34mm, tooth width = 11mm; driven gear : Number of teeth = 32, outer diameter = 61 mm, tooth width = 9 mm; pressure angle = 20? The material is 20CrMo, the surface of the gear is carburized and quenched, the carburizing depth is 0.30.5mm, and the hardness is 7883HRA.
Experimental equipment: magnetic filter arc source deposition system, JSM-5600LV scanning electron microscope, HV1000 micro hardness tester, etc.
2.1.2 Small gear coating The magnetic filter arc source deposition system is used to plate the CN film on the gear surface (the large gear is not coated).
2.1.3 Experimental Bench The power flow open bench was designed and built according to the experimental requirements and the actual situation of the laboratory, as shown in 1, 2 .
2.1.4 Experimental design This experiment uses ISOVG68 pure mechanical oil (without adding any additives) as lubricating oil. After assembly and commissioning, the temperature of the lubricating oil in the gearbox is monitored by the temperature sensor inserted into the lubricating oil pool. When the lubricating oil temperature is stable, the machine stops. The wear of the gear is checked through the opening at the top of the gearbox. Cool down to room temperature and increase the input torque in turn. Oil temperature and primary transmission efficiency were recorded every 10 minutes during the experiment (five data were recorded consecutively, averaged). The experimental speed is set to 1800r/min, the input torque starts from 4Nm, and the same experimental and experimental records are made for 8Nm, 11Nm, and 13Nm respectively. This part is regarded as the running-in process. After the experiment was completed, 12Nm was loaded and continuously turned on for 50 hours to perform destructive experiments.
For coated gears, if the coating has a large area of ​​wear during each stop inspection, it is considered as failure and the experiment is stopped. To prevent the wear debris from wearing the gears twice, change the oil each time it stops. Take two kinds of gears for experiment.
2.2 Experimental results and analysis 2.2.1 Metallographic photograph of the surface of the gear surface before and after the gear coating without metallization 1) Carburized and quenched gear Figure 3 shows the SEM image of the surface of the carburized and quenched gear ( 500 times), it can be clearly seen as tempered martensite, and the hardness of the gear surface is 628649HV (55HRC) by HV1000 microhardness tester.
2) The CN film is deposited on the surface of the carburized and quenched gear by the magnetic filter arc source deposition method, and the metallographic structure of the gear surface such as (800 times) and the metallographic structure of the gear core are shown as (800 times). . It can be seen from Fig. 5 that the metallographic structure of the gear surface is tempered martensite and tempered troostite. The test result of the gear surface with the hardness tester is 55HRC, and there is basically no change before the coating, and the core structure is Lath martensite. It can be seen that after 120 coating, the surface carburized and quenched layer structure is not affected, and the metallographic structure before and after plating is basically unchanged.
2.2.2 Wear of the gear surface The surface of the gear after the experiment was observed using a stereo microscope.
1) The coated gear has interference with the tooth root and the mating gear, the tooth surface coating is basically intact, and the large gear wear is also small, as shown in 6.
2) The uncoated gears have large and deep wear marks on the tooth faces of the small gears. It can be considered that the gears have failed, as shown in 7.
3 Conclusion The magnetic filter arc source deposition method (DFAD) can significantly improve the gear performance by plating CN film on the gear. The friction and wear experiments of the gears show that the metallographic structure and surface hardness of the front and rear gears of the coating are basically unchanged. The gear tooth surface of the CN film can significantly improve the friction and wear resistance. The reason is that the magnetic filter arc source is used. Deposition method The CN coating deposited on the surface of the gear is not only high in hardness, but also has a small friction factor and a low tendency to stick. Although the initial depth of ion implantation into the metal surface is shallow and the film is relatively thin, it can sustain the metal surface. The wear resistance is significantly improved. Coating the surface of the gear to improve the friction and wear resistance of the gear is very obvious and practical.
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